We are interested in gene expression and molecular pathogenesis of hepatitis B virus (HBV). In this proposal we will study: 1) the expression of the surface antigen (HBsAg) gene. The expression of the HBsAg gene is presumably regulated by two different promoters. Deletion mapping experiments will be performed to map these two promoters. Subsequently, the mapped -promoter sequences will be used in gel-retardation assays to characterize the protein factors that regulate these two promoters. 2) the transportation of HBsAg in cells and the assembly of 22nm HBsAg particles. We will mutate and express HBsAg proteins in order to study the functions of various domains of the HBsAg molecule on the transportation of HBsAg proteins in cells and on the assembly of 22nm particles. 3) the translocation of the core antigen (HBcAg) into membranes. The precore region of the HBcAg gene contains a signal peptide which can lead to the secretion of another HBV-related antigen, the e antigen, from cells. HBcAg with the precore region translated in vitro, however, cannot be translocated into microsomal membranes. We will fuse the HBcAg coding sequence to the preprolactin coding sequence and perform in vitro translation experiments to examine whether the precore region contains a defective signal peptide which requires helper factors to translocate HBcAg into membranes or the HBcAg sequence contains signals that inhibit its own translocation into membranes. 4) the nature of the polymerase gene product. The polymerase gene with or without the preceding HBcAg coding sequence will be expressed in mammalian cells. We will examine whether the polymerase is expressed as a HBcAg-pol fusion protein and whether post-translational processing is required for activating this enzyme. 5) the role of cytotoxic T-lymphocytes (CTL) in HBV-induced hepatitis. We will test the cytotoxicity of CTL isolated from chronic HBV carriers on HBV gene-transfected autologous fibroblasts. The goal of this project is to understand the mechanism of HBV-induced hepatitis. 6) the autocrine growth of hepG2 cells, a human hepatoma cell line. We will use biochemical methods to purify and characterize hepG2-derived autocrine factors.